The sixteenth century marks an important breaking point for the evolution of “Ottoman Sunnism.” Recent scholarship has discussed this change almost exclusively in light of the challenge that the Safavids posed to Ottoman legitimacy. However, the role of the Ottoman conquest of the Mamluk Sultanate and the encounter of the Ottoman and Mamluk scholars has not attracted the attention it deserves. Ottoman sultans and the scholar-bureaucrats may have tried to redefine Sunnism against the Safavid threat. Yet, they were perceived by some of the Mamluk scholars as newcomers to the Sunni tradition that long existed in the Arab lands. For them, the Ottomans were “not Sunni enough” and they were exceeding the limits of the Sharia and Sunna with certain practices, one of which was the act of “standing-up” during the recitation of the canto (bahir) about the Prophet’s birth in Mawlid ceremonies. An important and famous scholar, Ibrahim al-Halabi (d. 1549), who came from the Mamluk lands to Istanbul around 1500, criticized various customs of the “people of Rum” as overly affected by questionable Sufi practices. I will discuss the issue by focusing on al-Halabi’s treatise in which he criticized the practice of standing up during the Mawlid. Despite al-Halabi’s influence on Ottoman legal thought and practice, Ottomans kept on practicing this custom as a part of the state protocol in which sultans and high officials participated. The presentation aims to complicate the narratives about the emergence of “Ottoman Sunnism” by emphasizing the necessity of studying it in the context of Ottoman-Mamluk relations as well.